At and af in circuit breaker

In a circuit breaker, "AT" and "AF" are two important terms that refer to the trip characteristics of the breaker. Here's what they mean:

AT (Total Travel):

AT refers to the total distance the trip mechanism (usually a spring-loaded latch) travels from its initial position to its final position when the breaker trips. In other words, it's the total distance the breaker moves when it opens the circuit.

The AT value is typically measured in millimeters (mm) or inches (in) and is usually specified by the manufacturer. A higher AT value indicates that the breaker takes longer to trip, while a lower AT value indicates a faster trip.

AF (Fault Current):

AF stands for Fault Current, which is the maximum current that the breaker is designed to interrupt (or trip) when a fault occurs in the circuit. This value is usually specified in amperes (A) and is an important parameter in determining the breaker's rating and performance.

In other words, AF is the maximum current that the breaker can handle before it trips and opens the circuit to prevent damage to the equipment or personnel.

Here's an example:

Let's say a circuit breaker has an AT value of 10 mm and an AF value of 20 kA. This means that when a fault occurs in the circuit, the breaker will take approximately 10 mm to trip and open the circuit, and it's designed to interrupt currents up to 20,000 amperes (20 kA) before tripping.

In summary, AT and AF are two critical parameters that define the trip characteristics of a circuit breaker, with AT referring to the distance the breaker travels when tripping and AF referring to the maximum current the breaker can interrupt before tripping.